Tropical Climate Update

Madden–Julian Oscillation to weaken over Indian Ocean

A moderately strong pulse of the Madden–Julian Oscillation (MJO) has moved into the western Indian Ocean. It is expected to continue moving eastwards and weaken in the coming week, prior to reaching Maritime Continent longitudes, north of Australia. At this time of the year, an MJO pulse over the Indian Ocean typically reduces rainfall over parts of far northern Australia and the Maritime Continent.

Most climate models predict the MJO will continue to track east, and some predict it may be in a location that could favourably influence rainfall across northern Australia in the first or second week of December.

Read more about the Madden–Julian Oscillation

First tropical cyclone for southern hemisphere this season

Tropical atmospheric waves, including the MJO, on top of a favourable environment associated with the current La Niña, appear to have aided the formation of the first tropical cyclone (TC) to develop in the southern hemisphere for the 2020–21 TC season. Tropical cyclone Alicia developed in the South-West Indian Ocean last Saturday, 14 November, well east of Madagascar. Alicia peaked at an intensity equivalent to an Australian category 3 tropical cyclone but has recently commenced a weakening phase. It is forecast to weaken further as it moves to the southwest over the coming days, remaining well away from any significant land masses.

Tropical cyclone information and warnings for the South-West Indian Ocean is available from Meteo France

Above-average rainfall likely for northern Australia this wet season

Australian climate outlooks indicate a high chance (greater than 70%) of above-average rainfall across most of northern Australia in the December 2020 to March 2021 period. The rainfall outlooks are consistent with the ongoing La Niña, a seasonal climate driver typically associated with above-average rainfall across northern Australia during the wet season months of October to April.

Monsoon arrival (at Darwin) is normally earlier during La Niña, with an average date around mid-December, compared to the average date, a few days after Christmas.

The first tropical cyclone to form in the Australian region typically occurs about two weeks earlier than normal during La Niña years—based on data since 1970, the average date during La Niña years is mid-December. Tropical cyclone and tropical low frequency across northern Australia is often greater during La Niña, compared to non-La Niña years.

Recent climate models indicates the current La Niña is likely to persist until at least the end of February 2021. The Bureau's model, along with most of the surveyed international models, also predict the current La Niña is likely to be a relatively strong event, suggesting rainfall and flooding impacts may be relatively strong, based on historical precedents.

Read more about the El Niño-Southern Oscillation (ENSO)